Shedding and serological patterns of dairy cows following abortions associated with Coxiella burnetii DNA detection

To describe both shedding and serological patterns following abortions detected as being associated with Coxiella burnetii (Cb), 24 cows experiencing an abortion due to Cb were followed over a one month period. Samples taken on the day of abortion (D0) were followed 3-fold by weekly samplings from day 14 (D14) to D28 after the abortion. Milk and vaginal mucus were collected at each weekly sampling and tested using real-time PCR while blood samples were collected 2-fold on D21 and D28 and tested using ELISA. We found a very short duration of C. burnetii shedding in vaginal mucus after abortion, highlighting the need to collect samples as rapidly as possible following an abortion to avoid false negative results. In contrast with previous results, concomitancy of vaginal and mucus shedding was frequent, especially for cows shedding a high bacterial load on DO leading to the hypothesis that the clinical onset of the infection influences the modalities of Cb shedding. Lastly, serological results indicating a lack of sensitivity to detect Cb shedder cows (especially for cows for which Ct values were high) suggest that ELISA is not a useful tool to diagnose abortions at the individual level.